1. Field of the Invention
The present invention relates to a high-frequency package and, more particularly, to a high-frequency package accommodating a semiconductor device and a high-frequency circuit being formed on the periphery of the device, for which high-frequency signals in a band of quasi-millimeter wavelengths and about 30-90 GHz frequencies are used.
2. Description of the Relevant Art
A high-frequency package is constructed by a semiconductor device mounting area and a high-frequency circuit on the periphery of the device, and both are formed on a dielectric substrate, being hermetically sealed with a ring-shaped frame and a lid to be jointed thereon. High-frequency signals are input and output through signal lines passing through the bottom of the ring-shaped frame.
FIGS. 1a and 1b are schematic diagrams showing a conventional high-frequency package of this type, and FIG. 1a is a sectional side view, while FIG. 1b is a sectional perspective view along line Bxe2x80x94B of FIG. 1a. 
A dielectric substrate 41 is formed almost in the shape of a rectangular parallelepiped board having a thickness T. A ground 42 is formed on the bottom surface 41b of the dielectric substrate 41, while a ring-shaped frame 44 made of dielectrics is arranged in a prescribed place on the top surface 41a of the dielectric substrate 41. A plurality of thin-film-like circuit strips 43a having a width of w1 are formed in prescribed places on the top surface 41a in the inside region 44d of the frame 44, while lead strips 43b similar to those (having a width of w1) are formed outside the frame 44, facing the circuit strips 43a with the frame 44 between. One end portion of the circuit strip 43a and one end portion of the lead strip 43b are connected through a connecting strip 43c having a width of w2, which is buried under the frame 44. A signal line 43 includes these circuit strip 43a, lead strip 43b, and connecting strip 43c. 
In order to equalize the characteristic impedance of a circuit including the connecting strip 43c and the frame 44 thereabout to those of the circuit strip 43a and the lead strip 43b, the width w2 of the connecting strip 43c is set to be smaller than the widths w1 of the circuit strip 43a and the lead strip 43b. In order to hold down the return loss in the signal line 43 and to make the insertion loss smaller, each characteristic impedance in the circuit strip 43a, lead strip 43b and connecting strip 43c is matched to one another.
A semiconductor device 45 is mounted almost in the center of the frame inside region 44d on the top surface 41a, and pads 45a of the semiconductor device 45 and the circuit strips 43a are connected through bonding wires 45b. A lid 46 is jointed onto the top of the frame 44 (hermetic sealing), and the frame inside region 44d on the dielectric substrate 41 is hermetically sealed thereby. A high-frequency package 40 of a microstrip line includes the dielectric substrate 41, ground 42, signal lines 43, frame 44, lid 46, and associated parts.
High-frequency signals are input from the lead strip 43b of the signal line 43 through the connecting strip 43c and circuit strip 43a thereof and reach the semiconductor device 45, while high-frequency signals emitted from the semiconductor device 45 are output from the lead strip 43b of the signal line 43 through the circuit strip 43a and connecting strip 43c thereof.
However, in the high-frequency package 40 having that construction, the width w1 of the signal line 43 becomes narrow to w2 in the connecting strip 43c. As a result, it is difficult to secure the dimensional precision of w2, and the resistance increases in the connecting strip 43c, so that the insertion loss tends to be large. Moreover, in the manufacture thereof, it is difficult to accurately fit together both ends of the connecting strip 43c and the inner and outer surfaces 44b and 44c of the frame 44.
In order to cope with the problems, a high-frequency package has been proposed, wherein the portions of a frame, in which signal lines are buried, are formed to be thinner. FIG. 2 is a perspective view diagrammatically showing the principal part of a conventional high-frequency package of this type, and reference numerals 41 and 42 in the figure represent a dielectric substrate and a ground similar to those shown in FIG. 1. A ring-shaped frame 54 made of dielectrics is arranged in a prescribed place on the top surface 41a of the dielectric substrate 41, and an indented portion 54b is formed in a prescribed place of the frame 54 which a signal line 53 passes through. On the other hand, the thin-film-like signal line 53 having a width of w1 is formed in a prescribed place on the top surface 41a of the dielectric substrate 41. One end portion 53a of the signal line 53 is formed in the inside region 54d of the frame 54, while the other end portion 53b of the signal line 53 is formed in the outside region 54e of the frame 54. The middle portion of the signal line 53 is located in the vicinity of the indented portion 54b of the frame 54.
Since the other constructions are almost the same as those shown in FIG. 1, no detailed descriptions thereof are given here. A high-frequency package includes these dielectric substrate 41, ground 42, signal lines 53, frame 54, and associated parts. High-frequency signals are input through the signal line 53 to a semiconductor device 45 (FIG. 1), while high-frequency signals emitted from the semiconductor device 45 are output through the signal line 53.
However, in the high-frequency package having that construction, the thickness e1 of the indented portion 54b of the frame 54 need be set to be thin. This means that not only the manufacture thereof is difficult but the indented portion 54b thereof is especially low in strength.
In a high-frequency package of a microstrip line type shown in FIG. 1 or 2, when the semiconductor device 45 processes signals in a higher frequency band of such as millimeter or quasi-millimeter wavelengths, usually it causes a large connection loss of the semiconductor device 45 between the signal line 43 or 53, and a large radiation loss in the signal line 43 or 53 as well.
In order to cope with the problems, recently, a high-frequency package including a so-called coplanar line arrangement has been proposed, wherein signal lines and grounds are formed alongside next to each other on a dielectric substrate, and a semiconductor device 45 is mounted thereon in a flip-chip manner.
FIG. 3 is a perspective view partly in section diagrammatically showing the principal part of a conventional high-frequency package of this type (Japanese Kokai No. 02-87701), and in the figure, reference numeral 61 represents a metal substrate. A ceramic plate 63 is fixed on the metal substrate 61 in the shape of a rectangular parallelepiped board, and laminates 64 made by laminating, for example, three conductor layers 64a and three ceramic layers 64b alternately are attached in one piece on both left and right sides with the ceramic plate 63 between. A dielectric substrate 62 having an external shape of a rectangular parallelepiped board includes the ceramic plate 63, laminates 64, and associated parts. Thin-film-like signal lines 65 having a width of w1 are formed in prescribed places on the dielectric substrate 62 in the back-and-forth direction of the arrow in the figure, and grounds 66 are formed on both left and right sides of the signal lines 65 with gaps g interposed between.
Ceramic walls 68 are formed on the middle portions of the signal lines 65 and the grounds 66 thereabout in the right-and-left direction of the arrow in the figure, and laminates 69 made by laminating, for example, two conductor layers 69a and three ceramic layers 69b alternately are formed in one piece on both end portions of the ceramic walls 68. A frame 67 almost in the shape of the symbol # includes these ceramic walls 68 and laminates 69. The metal substrate 61 and the grounds 66 in the vicinity of the signal line 65 in the inside region 67a of the frame 67 are vertically connected through each one of conductive vias 66a on both left and right sides of the signal lines 65.
A metalized layer 71 is formed on the top of the frame 67, the front ends 64c and 69c, and the right ends 64d and 69d of the laminates 64 and 69, or the like. A high-frequency package of a coplanar line includes these dielectric substrate 62, signal lines 65, grounds 66, frame 67, metalized layer 71, and associated parts.
In the high-frequency package having that construction, a semiconductor device (not shown) is mounted in the inside region 67a of the frame 67. The signal lines 65, which are surrounded by the grounds 66, conductors 64a and 69a, metalized layer 71, and metal substrate 61, are electromagnetically shielded thereby. And the ring resonance of the signal lines 65 or the like is restricted by the laminates 64 and 69, or the like, so that it is possible to enhance the high-frequency characteristic in the band of quasi-millimeter wavelengths (30 GHz frequency or less).
However, in the high-frequency package of a coplanar line shown in FIG. 3, there likely to be a problem of an inferior high-frequency characteristic in the band exceeding 30 GHz frequency (quasi-millimeter wavelength band). It is difficult to reduce the thickness e0 of the ceramic wall 68, and it seems costly to manufacture the dielectric substrate 62 and the frame 67 having complicated constructions including the ceramic plate 63 or ceramic wall 68, and the laminate 64 or 69.
The present invention was developed in order to solve the above problems, and it is an object of the present invention to provide a high-frequency package, having an excellent high-frequency characteristic in a band from quasi-millimeter wavelengths to 90 GHz frequency range and a favorably sealed construction and excellent strength thereof, in addition, which can be easily manufactured at a competitive cost.
In order to achieve the above object, a high-frequency package (1) according to the present invention is characterized by having a ring-shaped frame,
first and second signal lines being formed so as to face each other with the ring-shaped frame between in the inside and outside regions separated by the ring-shaped frame, and
first and second grounds being formed around the first and second signal lines with gaps interposed between in the same plane, respectively, on one main surface side of a dielectric substrate;
having third signal lines, and
a third ground being formed around the third signal lines with gaps interposed between in the same plane on the other main surface side of the dielectric substrate;
wherein first conductive vias for vertically connecting each of one end portions of the first and second signal lines with both end portions of the third signal line are formed; and
a plurality of second conductive vias for vertically connecting the first and second grounds with the third ground are formed at prescribed intervals on both sides with the first to third signal lines between.
Here, the ring-shaped frame and the first and second grounds are conducting and it is desirable that both of the potentials thereof be zero.
In the high-frequency package (1), a signal interconnection in sequence including the first signal line, first conductive via, third signal line, first conductive via, and second signal line, can be easily formed not in contact with the frame, while a ground interconnection in sequence including the first ground, second conductive vias, third ground, second conductive vias, and second ground, can be easily formed. And a coplanar line including the ground interconnection and the signal interconnection can be formed.
The second conductive vias make it possible to reduce fluctuations in impedance based on the first conductive vias, resulting in a smaller return loss, while the electromagnetic waves emitted from the signal interconnection portion can be prevented from radiating into the dielectric substrate portion. As a result, the high-frequency characteristic in a band from quasi-millimeter to millimeter wavelengths can be excellent. Since the signal interconnection is kept from contact with the frame, it is possible to make the frame of a metal, which has the capability of electromagnetic shielding, leading to reliable sealing. As a result, a ground earth can be sufficiently established with the grounds, the ring-shaped frame, a lid, and associated parts, so that the stable transmission of high-frequency signals can be realized cost-effectively.
A high-frequency package (2) according to the present invention is characterized by setting a prescribed interval D between the second conductive vias within the range of
D less than xcex/(2xc3x97xcex5rxc2xd), 
Where
xcex5r is the dielectric constant of the dielectric substrate, and
xcex is the wavelength in the air of a high-frequency signal propagating through the first to third signal lines and first conductive vias.
Here, it is more favorable to make the lowest limit of the interval D as small as possible, but it is necessarily limited by the technique of forming the second conductive vias closer to each other on the dielectric substrate.
Using the high-frequency package (2), it is possible to prevent the high-frequency signals, emitted either from the first to third signal lines or first conductive vias in a direction perpendicular to the layers including the first to third signal lines, from leaking to the dielectric substrate portion through the narrower intervals D between the second conductive vias, so as to prevent the generation of ripples which seemingly is caused by the undesired mode originating in the wider intervals D. As a result, an excellent high-frequency characteristic in a high-frequency region of shorter wavelengths can be obtained.
A high-frequency package (3) according to the present invention is characterized by setting distances W between the first to third signal lines and the second conductive vias within the range of
W less than xcex(4xc3x97xcex5rxc2xd), 
Where
xcex5r is the dielectric constant of the dielectric substrate, and
xcex is the wavelength in the air of a high-frequency signal propagating through the first to third signal lines and first conductive vias in the high-frequency package (1) or (2).
Here, since the ripple generated by resonance has a certain band, in practice, it is desirable to estimate the distance W by substituting for xcex the wavelength equivalent to 1.15 times the wavelength that corresponds to the frequency of a high-frequency signal to be actually utilized.
It is more favorable to make the lowest limit of the distance W as small as possible, but it is necessarily limited by the widths of the first to third signal lines, the gaps, the diameter of the second conductive vias, or the like.
Using the high-frequency package (3), it is possible to prevent the occurrence of resonance originating in the distance W up to the second conductive via in the high-frequency signals, emitted either from the first to third signal lines or first conductive vias almost in a direction perpendicular to the layers including the first to third signal lines, and to prevent the generation of ripples. When the package (2) with the distance W set above is assumed to be used for a high-frequency package, its characteristic in a high-frequency band of much shorter wavelengths will be excellent due to a synergistic effect of the W and D.
A high-frequency package (4) according to the present invention is characterized by arranging the second conductive vias proximate to the first conductive vias on and/or outside arcs whose centers are the first conductive vias, having such a radius Ws as makes the relationship Ws greater than W hold,
where Ws is the distance between the center of the first conductive via and at least one of the second conductive vias proximate to the first conductive via, and
W are the distances between the second conductive vias, except the second conductive vias proximate to the first conductive vias, and the first to third signal lines in one of the high-frequency packages (1)-(3).
Here, when the distance Ws becomes larger, the electromagnetic radiation occurs, so that the insertion loss tends to be increased. Therefore, the distance Ws is desirably shorter than xcex/(2xc3x97xcex5rxc2xd), where xcex5r is the dielectric constant of the dielectric substrate, and xcex is the wavelength in the air of a high-frequency signal propagating through the first to third signal lines and first conductive vias.
Using the high-frequency package (4), the generation of ripples can be prevented and the return loss of signals to be transmitted through the first conductive vias can be reduced by the existence of the second conductive vias proximate to the first conductive vias. As a result, the insertion loss can be lowered.
A high-frequency package (5) according to the present invention is characterized by setting a distance L between the first conductive vias within the range of
2xc3x97T less than L less than xcex/(xcex5rxc2xd), 
where
xcex5r is the dielectric constant of the dielectric substrate,
xcex is the wavelength in the air of a high-frequency signal propagating through the first to third signal lines and first conductive vias, and
T is the thickness of the dielectric substrate in one of the high-frequency packages (1)-(4).
Here, since the ripple generated by resonance has a certain band, in practice, it is desirable to estimate the distance L by substituting for xcex the wavelength equivalent to 1.15 times the wavelength that corresponds to the frequency of a high-frequency signal to be actually utilized.
Using the high-frequency package (5), it is possible to prevent the occurrence of resonance which is inevitably caused by a longer distance L between the first conductive vias, so as to prevent the generation of ripples. And it is possible to restrict the interference of the electromagnetic field between the first conductive vias, which is inevitably caused by a shorter distance L, and it is also possible to restrict the generation of oscillations incident thereto. When the packages (2) and/or (3) with the distance L set above are used for a high-frequency package, their characteristic in a high-frequency region of still shorter wavelengths will be excellent due to a synergistic effect of the W, D and T.
A high-frequency package (6) according to the present invention is characterized by having a ring-shaped frame made of an insulating material,
first and second signal lines being formed so as to face each other with the ring-shaped frame between in the inside and outside regions separated by the ring-shaped frame, and
a first ground being formed around the first and second signal lines with gaps interposed between in the same plane on one main surface side of a dielectric substrate;
wherein at least one of the first and second signal lines is formed so as to partially lie under the ring-shaped frame;
having third signal lines, and
a second ground being formed around the third signal lines with gaps interposed between in the same plane on the other main surface side of the dielectric substrate;
wherein first conductive vias for vertically connecting each of one end portions of the first and second signal lines with both end portions of the third signal line are formed; and
a plurality of second conductive vias for vertically connecting the first ground with the second ground are formed at prescribed intervals on both sides with the first to third signal lines between.
In the high-frequency package (6), in addition to the effects described in the high-frequency package (1), the thickness of the ring-shaped frame can be set to be large, since at least one of the first and second signal lines may be formed so as to partially lie under the ring-shaped frame. Thus, the strength of the ring-shaped frame can be secured.
It is possible to form the ring-shaped frame made of an insulating material using the same kind of a ceramic as the constituent of a dielectric substrate. In this case, the formation of the ring-shaped frame and the dielectric substrate can be conducted in the same steps. The simplification of the manufacturing processes enables a reduction in cost.
A high-frequency package (7) according to the present invention is characterized by setting an interval D between the second conductive vias within the range of
D less than xcex/(2xc3x97xcex5rxc2xd), 
Where
xcex5r is the dielectric constant of the dielectric substrate, and
xcex is the wavelength in the air of a high-frequency signal propagating through the first to third signal lines and first conductive vias in the high-frequency package (6).
Using the high-frequency package (7), it is possible to prevent the high-frequency signals, emitted either from the first to third signal lines or first conductive vias in a direction perpendicular to the layers including the first to third signal lines from leaking to the dielectric substrate portion through the narrower intervals D between the second conductive vias, so as to prevent the generation of ripples which seemingly is caused by the undesired mode originating in the wider intervals D. As a result, an excellent high-frequency characteristic in a high-frequency region of shorter wavelengths can be obtained. Here, it is more favorable to make the lowest limit of the interval D as small as possible, but it is necessarily controlled by the technique of forming the second conductive vias closer to each other on the dielectric substrate.
A high-frequency package (8) according to the present invention is characterized by one main surface of the dielectric substrate except a semiconductor device mounting area and the vicinities of external input-output terminal portions, being covered with the ring-shaped frame of an insulating material in the high-frequency package (6) or (7).
Using the high-frequency package (8), the wall thickness of the ring-shaped frame made of an insulating material can be sufficiently large, so that a strength problem in the ring-shaped frame can be solved. By making the space for mounting a semiconductor device small, the cavity resonance can be suppressed.
A high-frequency package (9) according to the present invention is characterized by conductive vias for electromagnetic shielding, being formed in the interior of the ring-shaped frame made of an insulating material in one of the high-frequency packages (6)-(8).
In the case of the high-frequency package according to the present invention, it is possible to make the wall thickness of the ring-shaped frame of an insulating material sufficiently large. When the wall thickness of the ring-shaped frame of an insulating material is made sufficiently large, it is easy to form conductive vias for electromagnetic shielding in the interior of the ring-shaped frame. Since the conductive vias for such shielding are formed in the interior of the ring-shaped frame, the shielding effect on electromagnetic waves can be made still higher.
A high-frequency package (10) according to the present invention is characterized by a metalized layer, being formed on the top surface of the ring-shaped frame in one of the high-frequency packages (6)-(9).
In the high-frequency package (10), even if the ring-shaped frame comprises an insulator such as a ceramic, a lid made of Koval, invar, or the like can be easily jointed to the top of the ring-shaped frame.
A high-frequency package (11) according to the present invention is characterized by a plurality of semiconductor device mounting areas being formed on one main surface side of the dielectric substrate, while a plurality of openings for semiconductor device mounting being correspondingly formed in the ring-shaped frame, as a whole which is convertible to multichip module (MCM) packages in one of the high-frequency packages (6)-(10).
Using the high-frequency package (11), the conversion to MCM packages can be easily carried out as each kind of electronic element comes to meet the requirements of higher levels of function.